This invention relates to an improved method and apparatus for electrostatically drying a layer of wet material.
It is now well known from the U.S. patent to Stiles, U.S. Pat. No. 3,705,847, that a slurry of fluid and papermaking fibers can be passed between parallel adjacent runs of two continuous and looped conductive belt means which are charged to provide a potential differential therebetween and thereby cause the fibers in the slurry to form into a non-patterned, non-woven fiber mat on one of the belt means by an electrophoretic action while liquid is driven toward the other belt means by electro-osmosis so that the thus formed fiber mat can be transferred from its respective belt means to be further dried to form a dired sheet of paper or the like.
It is well known from the U.S. patent to Kalwaites, U.S. Pat. No. 2,862,251, that a slurry of fluid and natural or synthetic fibers can be formed into a continuous sheet in a conventional paper-making apparatus and before the resulting non-patterned fiber mat has been dried, jets of liquid can be forced through the fiber mat in combination with unique forming structure to cause the fibers in the fiber mat to be rearranged into a predetermined pattern comprising spaced interconnected packed fibrous portions with less dense or apertured portions therebetween whereby a patterned non-woven sheet is subsequently provided when the rearranged fiber mat is subsequently dried.
It is suggested in the U.S. patent to Candor et al., U.S. Pat. No. 3,757,426, and the various related U.S. patents referred to therein, that a slurry of fluid and papermaking fibers can be formed into a fibrous sheet by utilizing electrostatic means to remove liquid from such slurry during a paper-making operation or the like.
It is a feature of the invention of at least the aforementioned parent application, Ser. No. 405,023, to provide means for making a patterned non-woven sheet similar to the patterned sheets described in the aforementioned patent to Kalwaites by utilizing modified means of the aforementioned U.S. patents to Candor et al. and Stiles.
In particular, one embodiment of that invention provides a method and apparatus for making a patterned non-woven sheet by providing a slurry of fluid and fibers and forming that slurry into a sheet-like form. An electrostatic field action is created to act on such sheet-like form and cause the fibers thereof to be arranged into a predetermined pattern whereby a patterned non-woven sheet is provided.
It is another feature of that invention to provide an improved apparatus and method for making a non-woven sheet, whether or not such non-woven sheet is a patterned non-woven sheet or an unpatterned non-woven sheet, by providing improved means of the aforementioned Candor et al and Stiles arrangements.
In particular, one embodiment of that invention provides a method and apparatus for making a non-woven sheet from a slurry of fluid and fibers by passing a sheet-like form of such slurry between insulating faces of a pair of spaced apart electrode means that provide an electrostatic field action therebetween that acts on the sheet-like form to assist in the making of the non-woven sheet.
An embodiment of the invention of at least the aforementioned patent application, Ser. No. 541,218, provides a method and apparatus for making a non-woven sheet from a slurry of liquid and fibers by passing a sheet-like form of such slurry between two spaced apart surfaces while creating an electrostatic field action that acts on the sheet-like form between the two surfaces and causes at least part of the fibers to be arranged into a sheet adjacent one of the surfaces and at least part of the liquid to be arranged adjacent the other of the surfaces. Such embodiment of that invention can have means for causing at least part of the liquid to be drawn through the other surface at a controlled rate. Alternately or in addition thereto, such embodiment of that invention can be provided with needle-like projections on one of the surfaces to project at least partially into the sheet-like form disposed between the surfaces and assist the electrostatic field action in forming the sheet adjacent one of the surfaces.
Such needle-like projections are also believed to assist the electrostatic field action in removing liquid from the formed fibrous sheet because the projections are disposed closely adjacent the liquid remaining in the liquid bearing sheet of the aforementioned method and apparatus.
For example, see the December 1960 Scientific American article of H. A. Pohl at pages 107-116 wherein the author describes the feature of electrostatically pumping a dielectric liquid from a supply thereof by passing a fine wire electrode through the liquid reservoir and out of the same to cause the liquid to be driven up the wire electrode and off the end thereof at a rapid rate solely by the potential differential between the electrode and the liquid.
Thus, it is believed according to the invention set forth in at least the aforementioned patent application, Ser. No. 685,092 that such liquid removing action will also be effective in removing retained liquid from liquid bearing material of the liquid absorbing type by having the needle-like projections of that invention project completely through the liquid bearing material to assist in spraying liquid therefrom during the electrostatic liquid removing action thereon whether or not such material is being electrostatically formed, had been electrostatically formed, is being formed by other means or had been formed by other means and is merely to be dried.
Accordingly, it can be seen that the previously described needle-like projections can be utilized for a dual purpose, namely, to assist an electrostatic action in forming a layer of material from a slurry thereof and to assist an electrostatic action in removing retained liquid from a layer of material.
Therefore, it is a feature of the invention in the aforementioned patent application, Ser. No. 849,097, to illustrate, describe and claim a method and/or apparatus wherein such needle-like projections are utilized for one or both of the above functions.
In particular, it is believed that the layer forming and drying apparatus of the U.S. patent to Kunkle et al., U.S. Pat. No. 4,003,819 and/or of the U.S. patent to Inoue, U.S. Pat. No. 3,962,069 can be modified to include the needle-like projections of this invention to improve upon the electrostatic layer forming operation and/or the electrostatic layer drying operation thereof.
For example, one embodiment of that invention provides a method and apparatus for forming a layer of material against a movable conveying means from a slurry of a liquid and the material by an electrostatic action so that the layer of material can be subsequently removed in layer form from the conveying means, the method and apparatus including a plurality of needle-like projections disposed in the slurry to assist the electrostatic action in forming the layer of material from the slurry against the conveying means. Such needle-like projections can also be thereafter utilized to electrostatically move retained liquid in the thus formed layer of material to tend to remove liquid from the layer of material.
It is a feature of the invention in the aforementioned patent application, Ser. No. 085,216, to provide means for always causing the needle-like projections to completely project through the layer as the layer is being formed against one side of the conveying means in the above manner.
It is known from the article "Review of IPC research in high-intensity and thermal/vacuum drying processes" at pages 38 and 39 of the Oct. 15, 1981, Paper Trade Journal, that one way to provide a thermal/vacuum drying would be to confine the air-free wet paper web and felt between two steel bands after the wet paper web has been contacted by a highly heated member whereby one steel band that is heated will evaporate the liquid in the paper web and the evaporated liquid would condense back to a liquid on the other band that is cooled.
It is a feature of this invention to utilize the electrostatic drying means of the previously described methods and apparatus to augment the thermal/vacuum drying of the aforementioned article.
Accordingly, it is an object of this invention to provide an improved method of drying a layer of material, the method of this invention having one or more of the novel features of this invention as set forth above or hereinafter shown or described.
Another object of this invention is to provide an improved apparatus for drying a layer of material, the apparatus of this invention having one or more of the novel features of this invention as set forth above or hereinafter shown or described.
Other objects, uses and advantages of this invention are apparent from a reading of this description, which proceeds with reference to the accompanying drawings forming a part thereof and wherein: